In recent years, high-magnetic energy product permanent magnets have been developed by remarkable research and development on permanent magnets, and downsizing and increase in output of electric motors are being implemented.
In particular, in an electric motor to be used for a vehicle such as a hybrid automobile, a higher torque and a higher output are required to be obtained in a limited space. In order to achieve the higher torque and the higher output, the number of permanent magnets is required to increase a speed.
In this case, rotator core strength, which is required along with increase in centrifugal force, and cooling, which is required along with increase in loss density, become major problems.
Further, eddy currents generated on a surface of each of the permanent magnets increase along with the increased speed to generate heat. As a result, heat demagnetization (irreversible demagnetization) is caused to significantly lower performance such as efficiency of the electric motor, which becomes a serious problem.
Thus, a related-art electric motor includes a rotator core having a cooling hole formed to have a sectional shape that is convex to an outer circumferential side between a pair of permanent magnets opposed to each other in a V-like fashion. Refrigerant is caused to pass through the cooling hole to cool the rotator, thereby preventing the efficiency from being lowered due to temperature rise (see Patent Literature 1, for example).